Configuring and selecting the right access point is a crucial part of
setting up a functional multicast solution. In this section we will provide
advice on how we deal with various WiFi issues and how we configure our WiFi
access points to get the best possible performance.

If you have additional advice on how to improve WiFi multicast please
get in touch - we would love to talk with you: Contact Us.

WiFi access points announce their presence by sending out beacons,
however beacons are also used to announce whether it has traffic queued up
for power saving clients. This information is delivered inside a bitmap
in the beacon called the Traffic Indication Map (TIM).

The AP uses a special type of Traffic Indication Map (TIM) to to announce
that the it’s about to transmit all buffered broadcast and multicast frames
called the Delivery Traffic Indication Map (DTIM). Since all clients are
expected to receive broadcast/multicast traffic - all clients are expected
to wake up and listen for the traffic. How often a beacon includes a DTIM
is controlled by the DTIM period.

For these reasons you should consider the following configurations:

Setting the DTIM period to 1 will make every beacon a DTIM beacon.
Multicast/broadcast traffic will be sent after each beacon.

The OpenWrt option max_listen_int states the maximum number of beacons a
station (e.g. mobile device) may sleep before checking if data is pending.
Reducing this may keep devices awake to receive the broadcast packets more
often. If the option is set too low, the devices can not associate with the
access point. For some Huawei tablets the threshold seems to be 5, while
the Samsung galaxy s6 does not connect to the network if the value is below
10. Either way, in practice this option does not make devices stay awake
for more broadcast packets than usual.

Default multicast PHY rate varies from access point to access point. But,
the WiFi standard mandates that it be at least 1 Mbps for 2.4 Ghz and 6
Mbps for 5 Ghz. This is typically not enough for e.g. HD video streaming.
We therefore typically have to increase it. With OpenWrt we can do this
using the following approach:

When logged onto the access point e.g. via SSH the physical layer data rate
can be configured with the following command:

Using a 24 Mbps PHY rate the access point now runs stable. However, it does
not seem possible to increase the data rate to above ~7.2 Mbps (application
layer) before a major packet loss occur, even when forcing bitrates above
24 Mbps.